This invention relates to expression vectors comprising VEGF-D and its biologically active derivatives, cell lines stably expressing VEGF-D and its biologically active derivatives, and to a method of making a polypeptide using these expression vectors and host cells. The invention also relates to a method for treating and alleviating melanomas and various diseases.
Angiogenesis is a fundamental process required for normal growth and development of tissues, and involves the proliferation of new capillaries from pre-existing blood vessels. Angiogenesis is not only involved in embryonic development and normal tissue growth, repair, and regeneration, but is also involved in the female reproductive cycle, establishment and maintenance of pregnancy, and in repair of wounds and fractures. In addition to angiogenesis which takes place in the normal individual, angiogenic events are involved in a number of pathological processes, notably tumor growth and metastasis, and other conditions in which blood vessel proliferation, especially of the microvascular system, is increased, such as diabetic retinopathy, psoriasis and arthropathies. Inhibition of angiogenesis is useful in preventing or alleviating these pathological processes.
On the other hand, promotion of angiogenesis is desirable in situations where vascularization is to be established or extended, for example after tissue or organ transplantation, or to stimulate establishment of collateral circulation in tissue infarction or arterial stenosis, such as in coronary heart disease and thromboangitis obliterans.
Because of the crucial role of angiogenesis in so many physiological and pathological processes, factors involved in the control of angiogenesis have been intensively investigated. A number of growth factors have been shown to be involved in the regulation of angiogenesis; these include fibroblast growth factors (FGFs), platelet-derived growth factor (PDGF), transforming growth factor alpha (TGFα), and hepatocyte growth factor (HGF). See, for example, Folkman et al., J. Biol. Chem., 1992 267 10931-10934 for a review.
It has been suggested that a particular family of endothelial cell-specific growth factors and their corresponding receptors is primarily responsible for stimulation of endothelial cell growth and differentiation, and for certain functions of the differentiated cells. These factors are members of the PDGF family, and appear to act primarily via endothelial receptor tyrosine kinases (RTKs). Hitherto several vascular endothelial growth factor family members have been identified. Vascular endothelial growth factor (VEGF) is a homodimeric glycoprotein that has been isolated from several sources. VEGF shows highly specific mitogenic activity against endothelial cells, and can stimulate the whole sequence of events leading to angiogenesis. In addition, it has strong chemoattractant activity towards monocytes, can induce the plasminogen activator and the plasminogen activator inhibitor in endothelial cells, and can also influence microvascular permeability. Because of the latter activity, it is also sometimes referred to as vascular permeability factor (VPF). The isolation and properties of VEGF have been reviewed; see Ferrara et al., J. Cellular Biochem., 1991 47 211-218 and Connolly, J. Cellular Biochem., 1991 47 219-223.
More recently, six further members of the VEGF family have been identified. These are designated VEGF-B, described in International Patent Application PCT/US96/02957 (WO 96/26736) and in U.S. Pat. Nos. 5,840,693 and 5,607,918 by Ludwig Institute for Cancer Research and The University of Helsinki; VEGF-C, described in Joukov et al., The EMBO Journal, 1996 15 290-298; VEGF-D, described in International Patent Application No. PCT/US97/14696 (WO 98/07832); the placenta growth factor (PlGF), described in Maglione et al., Proc. Natl. Acad. Sci. USA, 1991 88 9267-9271; VEGF2, described in International Patent Application No. PCT/US94/05291 (WO 95/24473) by Human Genome Sciences, Inc; and VEGF3, described in International Patent Application No. PCT/US95/07283 (WO 96/39421) by Human Genome Sciences, Inc. Each show between 30% and 45% amino acid sequence identity with VEGF. The VEGF family members share a VEGF homology domain which contains the six cysteine residues which form the cysteine knot motif. Functional characteristics of the VEGF family include varying degrees of mitogenicity for endothelial cells, induction of vascular permeability and angiogenic and lymphangiogenic properties.
VEGF-B has similar angiogenic and other properties to those of VEGF, but is distributed and expressed in tissues differently from VEGF. In particular, VEGF-B is very strongly expressed in heart, and only weakly in lung, whereas the reverse is the case for VEGF. This suggests that VEGF and VEGF-B, despite the fact that they are co-expressed in many tissues, may have functional differences.
VEGF-B was isolated using a yeast co-hybrid interaction trap screening technique by screening for screening for cellular proteins which might interact with cellular retinoic acid-binding protein type I (CRABP-I). Its isolation and characteristics are described in detail in PCT/US96/02597 and in Olofsson et al., Proc. Natl. Acad. Sci. USA, 1996 93 2576-2581.
VEGF-C was isolated from conditioned media of PC-3 prostate adenocarcinoma cell line (CRL1435) by screening for ability of the medium to produce tyrosine phosphorylation of the endothelial cell-specific receptor tyrosine kinase VEGFR-3 (Flt4), using cells transfected to express VEGFR-3. VEGF-C was purified using affinity chromatography with recombinant VEGFR-3, and was cloned from a PC-3 cDNA library. Its isolation and characteristics are described in detail in Joukov et al., The EMBO Journal, 1996 15 290-298.
VEGF-D was isolated from a human breast cDNA library, commercially available from Clontech, by screening with an expressed sequence tag obtained from a human cDNA library designated “Soares Breast 3NbHBst” as a hybridization probe (Achen et al., Proc. Natl. Acad. Sci. USA, 1998 95 548-553). Its isolation and characteristics are described in detail in International Patent Application No. PCT/US97/14696.
In PCT/US97/14696, the isolation of a biologically active fragment of VEGF-D, designated VEGF-DΔNΔC, is also described. This fragment consists of VEGF-D amino acid residues 93 to 201 of SEQ ID NO: 11 (which corresponds to SEQ ID NO: 5 of PCT/US97/14696) linked to the affinity tag peptide FLAG®. The entire disclosure of the International Patent Application PCT/US97/14696 (WO 98/07832) is incorporated herein by reference.
VEGF-D has structural similarities to other members of the VEGF family. However, despite these structural similarities, it is structurally and functionally distinguished from other members of VEGF family. Human VEGF-D is only 48% identical to VEGF-C, which is the member of the family to which VEGF-D is most closely related.
The VEGF-D gene is broadly expressed in the adult human, but is certainly not ubiquitously expressed. VEGF-D is strongly expressed in heart, lung and skeletal muscle. Intermediate levels of VEGF-D are expressed in spleen, ovary, small intestine and colon, and a lower expression occurs in kidney, pancreas, thymus, prostate and testis. No VEGF-D mRNA was detected in RNA from brain, placenta, liver or peripheral blood leukocytes.
PlGF was isolated from a term placenta cDNA library. Its isolation and characteristics are described in detail in Maglione et al., Proc. Natl. Acad. Sci. USA, 1991 88 9267-9271. Presently its biological function is not well understood.
VEGF2 was isolated from a highly tumorgenic, oestrogen-independent human breast cancer cell line. While this molecule is stated to have about 22% homology to PDGF and 30% homology to VEGF, the method of isolation of the gene encoding VEGF2 is unclear, and no characterization of the biological activity is disclosed.
VEGF3 was isolated from a cDNA library derived from colon tissue. VEGF3 is stated to have about 36% identity and 66% similarity to VEGF. The method of isolation of the gene encoding VEGF3 is unclear and no characterization of the biological activity is disclosed.
Vascular endothelial growth factors appear to act primarily by binding to receptor tyrosine kinases. Five endothelial cell-specific receptor tyrosine kinases have been identified, namely VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1), VEGFR-3 (Flt4), Tie and Tek/Tie-2. All of these have the intrinsic tyrosine kinase activity which is necessary for signal transduction. The essential, specific role in vasculogenesis and angiogenesis of VEGFR-1, VEGFR-2, VEGFR-3, Tie and Tek/Tie-2 has been demonstrated by targeted mutations inactivating these receptors in mouse embryos.
The only receptor tyrosine kinases known to bind VEGFs are VEGFR-1, VEGFR-2 and VEGFR-3. VEGFR-1 and VEGFR-2 bind VEGF with high affinity, and VEGFR-1 also binds VEGF-B. VEGF-C has been shown to be the ligand for VEGFR-3, and also activates VEGFR-2 (Joukov et al., The EMBO Journal, 1996 15 290-298). VEGF-D shares receptor specificity with VEGF-C (Achen et al., Proc. Natl. Acad. Sci. USA, 1998 95 548-553). A ligand for Tek/Tie-2 has been described (International Patent Application PCT/US95/12935 (WO 96/11269) by Regeneron Pharmaceuticals, Inc.); however, the ligand for Tie has not yet been identified.
The primary translation products of VEGF-D and VEGF-C have long -and C-terminal polypeptide extensions in addition to a central VEGF homology domain (VHD). In the case of VEGF-C, these polypeptide extensions are propeptides which are proteolytically cleaved to generate a secreted form which consists only of the VHD and is capable of binding to VEGFR-2 and VEGFR-3 (Joukov et al., The EMBO Journal, 1996 15 290-298; Joukov et al., EMBO J., 1997 16 3898-3911). Likewise, a recombinant form of VEGF-D, consisting only of the VHD, was shown to bind and activate these receptors and to be mitogenic for endothelial cells, although VEGF-D processing was uncharacterized (Achen et al., Proc. Natl. Acad. Sci. USA, 1998 95 548-553).
Recently, a novel 130-135 kDa VEGF-A isoform specific receptor has been purified and cloned (Soker et al., Cell, 1998 92 735-745). The VEGF receptor was found to bind specifically the VEGF-A165 isoform via the exon 7 encoded sequence, which shows weak affinity for heparin (Soker et al., Cell, 1998 92 735-745). Surprisingly, the receptor was shown to be identical to human neuropilin-1 (NP-1), a receptor involved in early stage neuromorphogenesis. PlGF-2 also appears to interact with NP-1 (Migdal et al., J. Biol. Chem., 1998 273 22272-22278).
Gene targeting studies have demonstrated the absolute requirement of VEGFR-1, VEGFR-2 and VEGFR-3 for embryonic development. These studies show that VEGFR-1 plays a role in vascular endothelial tube formation, VEGFR-2 is important for endothelial/hematopoietic cell differentiation and mitogenesis, and VEGFR-3 is involved in regulation of vascular remodeling, the formation of large vessels and in lymphangiogenesis. The functions of these receptors are reviewed in Mustonen and Alitalo, J. Cell Biol., 1995 129 895-898.
The VEGFR-3 is expressed in venous and lymphatic endothelia in the fetus, and predominantly in lymphatic endothelia in the adult (Kaipainen et al., Cancer Res, 1994 54 6571-6577; Proc. Natl. Acad. Sci. USA, 1995 92 3566-3570). VEGFR-3 has an essential role in the development of the embryonic cardiovascular system before the emergence of the lymphatic vessels (Dumont et al., Science, 1998 282 946-949). It has been suggested that VEGF-C may have a primary function in lymphatic endothelium, and a secondary function in angiogenesis and permeability regulation which is shared with VEGF (Joukov et al., The EMBO Journal, 1996 290-298).